Google just released an update to their Maps app for Android, and it has offline access to whatever maps you may want on hand.

Google's offline access supports over 150 countries, and can store up to six large metro areas (like greater London, Paris, or New York City and surrounding area) on your device for access when you don't have a connection. It's great for those times you're stuck in an area with no service and need to navigate home, or if you're traveling overseas and don't have an international data connection. GPS will still work without data, since it's a separate connection, and you can navigate yourself anywhere within that saved area. The new version of Maps also has a smoother compass mode in Street View, for devices that have the feature available.